What is going wrong in this circuit which supposedly should step down AC to arduino friendly voltage?
$begingroup$
So I'm using this circuit
but when adapter output is disconnected and only midpoint terminal of the transformer is connected the Arduino input pin reads some mV. mid point reads perfect 2.5V. What am I doing wrong?
arduino transformer ac
asked Mar 23 at 12:19
Vibhore JainVibhore Jain
8817
$endgroup$
|
show 1 more comment
$begingroup$
So I'm using this circuit
but when adapter output is disconnected and only midpoint terminal of the transformer is connected the Arduino input pin reads some mV. mid point reads perfect 2.5V. What am I doing wrong?
arduino transformer ac
asked Mar 23 at 12:19
Vibhore JainVibhore Jain
8817
$endgroup$
2
$begingroup$
Reads some mV relative to what? Arduino ground? If so, you either have a short to ground somewhere, you are accidentally driving the pin low, or you have killed the I/O pin.
$endgroup$
– jms
Mar 23 at 12:30
1
$begingroup$
Double-check your wiring. If you built this on a breadboard socket, it's possible you have a wire in a hole next to the one it actually belongs in. It happens more often than you might think.
$endgroup$
– Dave Tweed♦
Mar 23 at 12:43
2
$begingroup$
What's the winding ratio of your "AC-AC adapter" (which I'd prefer to call a "transformer").
$endgroup$
– Marcus Müller
Mar 23 at 12:46
1
$begingroup$
Please re-write you question using separate sentences to describe which conditions work and which conditions do not work. Does the circuit work correctly when the AC adapter is connected and powered up? Does the circuit work correctly when the AC adapter is connected but not powered? What is the input impedance of the Arduino analog input pin?
$endgroup$
– AnalogKid
Mar 23 at 14:15
1
$begingroup$
Disconnect the Arduino pin, leave everything else, and make a measurement at the voltage divider output. Divide and conquer.
$endgroup$
– Spehro Pefhany
Mar 23 at 19:51
|
show 1 more comment
$begingroup$
So I'm using this circuit
but when adapter output is disconnected and only midpoint terminal of the transformer is connected the Arduino input pin reads some mV. mid point reads perfect 2.5V. What am I doing wrong?
arduino transformer ac
asked Mar 23 at 12:19
Vibhore JainVibhore Jain
8817
$endgroup$
So I'm using this circuit
but when adapter output is disconnected and only midpoint terminal of the transformer is connected the Arduino input pin reads some mV. mid point reads perfect 2.5V. What am I doing wrong?
arduino transformer ac
arduino transformer ac
asked Mar 23 at 12:19
Vibhore JainVibhore Jain
8817
asked Mar 23 at 12:19
Vibhore JainVibhore Jain
8817
asked Mar 23 at 12:19
Vibhore JainVibhore Jain
8817
asked Mar 23 at 12:19
Vibhore JainVibhore Jain
8817
asked Mar 23 at 12:19
Vibhore JainVibhore Jain
8817
8817
2
$begingroup$
Reads some mV relative to what? Arduino ground? If so, you either have a short to ground somewhere, you are accidentally driving the pin low, or you have killed the I/O pin.
$endgroup$
– jms
Mar 23 at 12:30
1
$begingroup$
Double-check your wiring. If you built this on a breadboard socket, it's possible you have a wire in a hole next to the one it actually belongs in. It happens more often than you might think.
$endgroup$
– Dave Tweed♦
Mar 23 at 12:43
2
$begingroup$
What's the winding ratio of your "AC-AC adapter" (which I'd prefer to call a "transformer").
$endgroup$
– Marcus Müller
Mar 23 at 12:46
1
$begingroup$
Please re-write you question using separate sentences to describe which conditions work and which conditions do not work. Does the circuit work correctly when the AC adapter is connected and powered up? Does the circuit work correctly when the AC adapter is connected but not powered? What is the input impedance of the Arduino analog input pin?
$endgroup$
– AnalogKid
Mar 23 at 14:15
1
$begingroup$
Disconnect the Arduino pin, leave everything else, and make a measurement at the voltage divider output. Divide and conquer.
$endgroup$
– Spehro Pefhany
Mar 23 at 19:51
|
show 1 more comment
2
$begingroup$
Reads some mV relative to what? Arduino ground? If so, you either have a short to ground somewhere, you are accidentally driving the pin low, or you have killed the I/O pin.
$endgroup$
– jms
Mar 23 at 12:30
1
$begingroup$
Double-check your wiring. If you built this on a breadboard socket, it's possible you have a wire in a hole next to the one it actually belongs in. It happens more often than you might think.
$endgroup$
– Dave Tweed♦
Mar 23 at 12:43
2
$begingroup$
What's the winding ratio of your "AC-AC adapter" (which I'd prefer to call a "transformer").
$endgroup$
– Marcus Müller
Mar 23 at 12:46
1
$begingroup$
Please re-write you question using separate sentences to describe which conditions work and which conditions do not work. Does the circuit work correctly when the AC adapter is connected and powered up? Does the circuit work correctly when the AC adapter is connected but not powered? What is the input impedance of the Arduino analog input pin?
$endgroup$
– AnalogKid
Mar 23 at 14:15
1
$begingroup$
Disconnect the Arduino pin, leave everything else, and make a measurement at the voltage divider output. Divide and conquer.
$endgroup$
– Spehro Pefhany
Mar 23 at 19:51
2
2
$begingroup$
Reads some mV relative to what? Arduino ground? If so, you either have a short to ground somewhere, you are accidentally driving the pin low, or you have killed the I/O pin.
$endgroup$
– jms
Mar 23 at 12:30
$begingroup$
Reads some mV relative to what? Arduino ground? If so, you either have a short to ground somewhere, you are accidentally driving the pin low, or you have killed the I/O pin.
$endgroup$
– jms
Mar 23 at 12:30
1
1
$begingroup$
Double-check your wiring. If you built this on a breadboard socket, it's possible you have a wire in a hole next to the one it actually belongs in. It happens more often than you might think.
$endgroup$
– Dave Tweed♦
Mar 23 at 12:43
$begingroup$
Double-check your wiring. If you built this on a breadboard socket, it's possible you have a wire in a hole next to the one it actually belongs in. It happens more often than you might think.
$endgroup$
– Dave Tweed♦
Mar 23 at 12:43
2
2
$begingroup$
What's the winding ratio of your "AC-AC adapter" (which I'd prefer to call a "transformer").
$endgroup$
– Marcus Müller
Mar 23 at 12:46
$begingroup$
What's the winding ratio of your "AC-AC adapter" (which I'd prefer to call a "transformer").
$endgroup$
– Marcus Müller
Mar 23 at 12:46
1
1
$begingroup$
Please re-write you question using separate sentences to describe which conditions work and which conditions do not work. Does the circuit work correctly when the AC adapter is connected and powered up? Does the circuit work correctly when the AC adapter is connected but not powered? What is the input impedance of the Arduino analog input pin?
$endgroup$
– AnalogKid
Mar 23 at 14:15
$begingroup$
Please re-write you question using separate sentences to describe which conditions work and which conditions do not work. Does the circuit work correctly when the AC adapter is connected and powered up? Does the circuit work correctly when the AC adapter is connected but not powered? What is the input impedance of the Arduino analog input pin?
$endgroup$
– AnalogKid
Mar 23 at 14:15
1
1
$begingroup$
Disconnect the Arduino pin, leave everything else, and make a measurement at the voltage divider output. Divide and conquer.
$endgroup$
– Spehro Pefhany
Mar 23 at 19:51
$begingroup$
Disconnect the Arduino pin, leave everything else, and make a measurement at the voltage divider output. Divide and conquer.
$endgroup$
– Spehro Pefhany
Mar 23 at 19:51
|
show 1 more comment
6 Answers
6
active
oldest
votes
$begingroup$
Trash will couple from primary to secondary, at frequencies the opamp cannot control.
How about this
simulate this circuit – Schematic created using CircuitLab
answered Mar 23 at 14:11
analogsystemsrfanalogsystemsrf
15.9k2822
$endgroup$
4
$begingroup$
Care to explain why this is better than the other one? and something about what it does?
$endgroup$
– laptop2d
Mar 23 at 19:33
1
$begingroup$
Its just a transformer followed by a high pass filter. Not sure why'd you use a high pass filter to try and eliminate HF noise though.
$endgroup$
– Stiddily
Mar 23 at 22:41
add a comment |
$begingroup$
That's the normal behavior for the circuit you posted. Your adc can read voltages from 0 to 5v but the ac signal (if the voltage divider is spot on) is -2.5v to 2.5v. So you mix a dc 2.5v with the ac signal and subtract the offset voltage the arduino measures to reference your measurement circuits ac 'ground' reference. So 0-127 will be negative and 128-255 will be positive. Openenergymonitor project has some great tutorials and sample code that may keep you from killing yourself literally or figuratively figuring this stuff out.
The buffer opamp isn't needed in your circuit as you are not using much current from the reference voltage. Just Capacitor c1 would give the 2.5v divider a clean voltage. A 3pin 2.5v Ldo chip would give a more accurate reference but is overkill for a toss off arduino circuit.
But I think the real answer to your question is that you should use ac voltage setting on your meter to test the circuit. if you use a meter in DC mode with the mains plugged the voltage will be 0 as the average of a sine wave and 2.5v with no mains signal as that is your 'ground' voltage not 0v.
answered Mar 24 at 4:24
Michael ValliantMichael Valliant
111
$endgroup$
add a comment |
$begingroup$
When you disconnect the adapter there is no current flowing in secondary coil, as there are two 12k resistors which make voltage divider by ratio of 1:2 so in the mid point of it there will be 2.5 v which is applied to the non inverting terminal of op amp which is set to unity gain so the output of op-amp will b 2.5v and as the is no current flowing in the resistor R1 the voltage drop will be 0v so the 2.5v is seen on the Arduino Input pin.
answered Mar 23 at 20:23
Yash JasnaniYash Jasnani
1
$endgroup$
add a comment |
$begingroup$
The 'non-midpoint' ground of the secondary transformer should have the same potential as the ground of the Arduino just like analogsystemsrf has done. Otherwise, who knows what kind of voltages you could see at the ADC of the Arduino?
Also, since this is AC, and the 'positive/top' side of the transformer would go negative with respect to the secondary ground, so you need a rectifier so the ADC pin does not go below ground. A series cap like analogsystemsrf would eliminate DC bias.
Edit: Another method (without rectifying) is to add a DC bias of 2.5V so that the signal goes above and below 2.5V (but not abober 5V or below 0V) you could then read both the positive and negative signal while maintaining a safe 0-5V for the ADC. Look up adding a DC bias on Google for many references, but it's basically a voltage divider with the midpoint connected to the signal you want to bias.
answered Mar 23 at 22:55
AdvancedNewbieAdvancedNewbie
33
$endgroup$
add a comment |
$begingroup$
if u r measuring Ac Voltage corresponding to AC Main i will suggest u please used diode bridge and filter capacitor at secondary side.
1. u will get DC voltage corresponding to AC mains
2. In your circuit opamp o/p getting loaded because of transformer secondary winding when your AC Mains not available. that's why your reference is changing.
answered Mar 24 at 2:58
Aditya Suresh RajpurkarAditya Suresh Rajpurkar
1
$endgroup$
add a comment |
$begingroup$
Where did you get the circuit? I'd like to see the original. It will not work at all as drawn.
If all you want is 5v you just need your transformer connected to a bridge rectifier. The low output of the bridge rectifier will be your ground. Then you connect a 7805 regulator and a cap before and after and walla! You have a nice 5v 1A power supply.
(https://i.stack.imgur.com/eiwzE.png)
answered Mar 24 at 17:32
TpKnetTpKnet
1015
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1
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It's not a power supply. OP is presumably trying to isolate, step down, and bias the mains voltage to midscale for the analog-to-digital input.
$endgroup$
– Spehro Pefhany
Mar 24 at 17:42
add a comment |
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6 Answers
6
active
oldest
votes
6 Answers
6
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Trash will couple from primary to secondary, at frequencies the opamp cannot control.
How about this
simulate this circuit – Schematic created using CircuitLab
answered Mar 23 at 14:11
analogsystemsrfanalogsystemsrf
15.9k2822
$endgroup$
4
$begingroup$
Care to explain why this is better than the other one? and something about what it does?
$endgroup$
– laptop2d
Mar 23 at 19:33
1
$begingroup$
Its just a transformer followed by a high pass filter. Not sure why'd you use a high pass filter to try and eliminate HF noise though.
$endgroup$
– Stiddily
Mar 23 at 22:41
add a comment |
$begingroup$
Trash will couple from primary to secondary, at frequencies the opamp cannot control.
How about this
simulate this circuit – Schematic created using CircuitLab
answered Mar 23 at 14:11
analogsystemsrfanalogsystemsrf
15.9k2822
$endgroup$
4
$begingroup$
Care to explain why this is better than the other one? and something about what it does?
$endgroup$
– laptop2d
Mar 23 at 19:33
1
$begingroup$
Its just a transformer followed by a high pass filter. Not sure why'd you use a high pass filter to try and eliminate HF noise though.
$endgroup$
– Stiddily
Mar 23 at 22:41
add a comment |
$begingroup$
Trash will couple from primary to secondary, at frequencies the opamp cannot control.
How about this
simulate this circuit – Schematic created using CircuitLab
answered Mar 23 at 14:11
analogsystemsrfanalogsystemsrf
15.9k2822
$endgroup$
Trash will couple from primary to secondary, at frequencies the opamp cannot control.
How about this
simulate this circuit – Schematic created using CircuitLab
answered Mar 23 at 14:11
analogsystemsrfanalogsystemsrf
15.9k2822
edited Mar 25 at 3:54
answered Mar 23 at 14:11
analogsystemsrfanalogsystemsrf
15.9k2822
answered Mar 23 at 14:11
analogsystemsrfanalogsystemsrf
15.9k2822
answered Mar 23 at 14:11
analogsystemsrfanalogsystemsrf
15.9k2822
15.9k2822
4
$begingroup$
Care to explain why this is better than the other one? and something about what it does?
$endgroup$
– laptop2d
Mar 23 at 19:33
1
$begingroup$
Its just a transformer followed by a high pass filter. Not sure why'd you use a high pass filter to try and eliminate HF noise though.
$endgroup$
– Stiddily
Mar 23 at 22:41
add a comment |
4
$begingroup$
Care to explain why this is better than the other one? and something about what it does?
$endgroup$
– laptop2d
Mar 23 at 19:33
1
$begingroup$
Its just a transformer followed by a high pass filter. Not sure why'd you use a high pass filter to try and eliminate HF noise though.
$endgroup$
– Stiddily
Mar 23 at 22:41
4
4
$begingroup$
Care to explain why this is better than the other one? and something about what it does?
$endgroup$
– laptop2d
Mar 23 at 19:33
$begingroup$
Care to explain why this is better than the other one? and something about what it does?
$endgroup$
– laptop2d
Mar 23 at 19:33
1
1
$begingroup$
Its just a transformer followed by a high pass filter. Not sure why'd you use a high pass filter to try and eliminate HF noise though.
$endgroup$
– Stiddily
Mar 23 at 22:41
$begingroup$
Its just a transformer followed by a high pass filter. Not sure why'd you use a high pass filter to try and eliminate HF noise though.
$endgroup$
– Stiddily
Mar 23 at 22:41
add a comment |
$begingroup$
That's the normal behavior for the circuit you posted. Your adc can read voltages from 0 to 5v but the ac signal (if the voltage divider is spot on) is -2.5v to 2.5v. So you mix a dc 2.5v with the ac signal and subtract the offset voltage the arduino measures to reference your measurement circuits ac 'ground' reference. So 0-127 will be negative and 128-255 will be positive. Openenergymonitor project has some great tutorials and sample code that may keep you from killing yourself literally or figuratively figuring this stuff out.
The buffer opamp isn't needed in your circuit as you are not using much current from the reference voltage. Just Capacitor c1 would give the 2.5v divider a clean voltage. A 3pin 2.5v Ldo chip would give a more accurate reference but is overkill for a toss off arduino circuit.
But I think the real answer to your question is that you should use ac voltage setting on your meter to test the circuit. if you use a meter in DC mode with the mains plugged the voltage will be 0 as the average of a sine wave and 2.5v with no mains signal as that is your 'ground' voltage not 0v.
answered Mar 24 at 4:24
Michael ValliantMichael Valliant
111
$endgroup$
add a comment |
$begingroup$
That's the normal behavior for the circuit you posted. Your adc can read voltages from 0 to 5v but the ac signal (if the voltage divider is spot on) is -2.5v to 2.5v. So you mix a dc 2.5v with the ac signal and subtract the offset voltage the arduino measures to reference your measurement circuits ac 'ground' reference. So 0-127 will be negative and 128-255 will be positive. Openenergymonitor project has some great tutorials and sample code that may keep you from killing yourself literally or figuratively figuring this stuff out.
The buffer opamp isn't needed in your circuit as you are not using much current from the reference voltage. Just Capacitor c1 would give the 2.5v divider a clean voltage. A 3pin 2.5v Ldo chip would give a more accurate reference but is overkill for a toss off arduino circuit.
But I think the real answer to your question is that you should use ac voltage setting on your meter to test the circuit. if you use a meter in DC mode with the mains plugged the voltage will be 0 as the average of a sine wave and 2.5v with no mains signal as that is your 'ground' voltage not 0v.
answered Mar 24 at 4:24
Michael ValliantMichael Valliant
111
$endgroup$
add a comment |
$begingroup$
That's the normal behavior for the circuit you posted. Your adc can read voltages from 0 to 5v but the ac signal (if the voltage divider is spot on) is -2.5v to 2.5v. So you mix a dc 2.5v with the ac signal and subtract the offset voltage the arduino measures to reference your measurement circuits ac 'ground' reference. So 0-127 will be negative and 128-255 will be positive. Openenergymonitor project has some great tutorials and sample code that may keep you from killing yourself literally or figuratively figuring this stuff out.
The buffer opamp isn't needed in your circuit as you are not using much current from the reference voltage. Just Capacitor c1 would give the 2.5v divider a clean voltage. A 3pin 2.5v Ldo chip would give a more accurate reference but is overkill for a toss off arduino circuit.
But I think the real answer to your question is that you should use ac voltage setting on your meter to test the circuit. if you use a meter in DC mode with the mains plugged the voltage will be 0 as the average of a sine wave and 2.5v with no mains signal as that is your 'ground' voltage not 0v.
answered Mar 24 at 4:24
Michael ValliantMichael Valliant
111
$endgroup$
That's the normal behavior for the circuit you posted. Your adc can read voltages from 0 to 5v but the ac signal (if the voltage divider is spot on) is -2.5v to 2.5v. So you mix a dc 2.5v with the ac signal and subtract the offset voltage the arduino measures to reference your measurement circuits ac 'ground' reference. So 0-127 will be negative and 128-255 will be positive. Openenergymonitor project has some great tutorials and sample code that may keep you from killing yourself literally or figuratively figuring this stuff out.
The buffer opamp isn't needed in your circuit as you are not using much current from the reference voltage. Just Capacitor c1 would give the 2.5v divider a clean voltage. A 3pin 2.5v Ldo chip would give a more accurate reference but is overkill for a toss off arduino circuit.
But I think the real answer to your question is that you should use ac voltage setting on your meter to test the circuit. if you use a meter in DC mode with the mains plugged the voltage will be 0 as the average of a sine wave and 2.5v with no mains signal as that is your 'ground' voltage not 0v.
answered Mar 24 at 4:24
Michael ValliantMichael Valliant
111
answered Mar 24 at 4:24
Michael ValliantMichael Valliant
111
answered Mar 24 at 4:24
Michael ValliantMichael Valliant
111
answered Mar 24 at 4:24
Michael ValliantMichael Valliant
111
111
add a comment |
add a comment |
$begingroup$
When you disconnect the adapter there is no current flowing in secondary coil, as there are two 12k resistors which make voltage divider by ratio of 1:2 so in the mid point of it there will be 2.5 v which is applied to the non inverting terminal of op amp which is set to unity gain so the output of op-amp will b 2.5v and as the is no current flowing in the resistor R1 the voltage drop will be 0v so the 2.5v is seen on the Arduino Input pin.
answered Mar 23 at 20:23
Yash JasnaniYash Jasnani
1
$endgroup$
add a comment |
$begingroup$
When you disconnect the adapter there is no current flowing in secondary coil, as there are two 12k resistors which make voltage divider by ratio of 1:2 so in the mid point of it there will be 2.5 v which is applied to the non inverting terminal of op amp which is set to unity gain so the output of op-amp will b 2.5v and as the is no current flowing in the resistor R1 the voltage drop will be 0v so the 2.5v is seen on the Arduino Input pin.
answered Mar 23 at 20:23
Yash JasnaniYash Jasnani
1
$endgroup$
add a comment |
$begingroup$
When you disconnect the adapter there is no current flowing in secondary coil, as there are two 12k resistors which make voltage divider by ratio of 1:2 so in the mid point of it there will be 2.5 v which is applied to the non inverting terminal of op amp which is set to unity gain so the output of op-amp will b 2.5v and as the is no current flowing in the resistor R1 the voltage drop will be 0v so the 2.5v is seen on the Arduino Input pin.
answered Mar 23 at 20:23
Yash JasnaniYash Jasnani
1
$endgroup$
When you disconnect the adapter there is no current flowing in secondary coil, as there are two 12k resistors which make voltage divider by ratio of 1:2 so in the mid point of it there will be 2.5 v which is applied to the non inverting terminal of op amp which is set to unity gain so the output of op-amp will b 2.5v and as the is no current flowing in the resistor R1 the voltage drop will be 0v so the 2.5v is seen on the Arduino Input pin.
answered Mar 23 at 20:23
Yash JasnaniYash Jasnani
1
answered Mar 23 at 20:23
Yash JasnaniYash Jasnani
1
answered Mar 23 at 20:23
Yash JasnaniYash Jasnani
1
answered Mar 23 at 20:23
Yash JasnaniYash Jasnani
1
1
add a comment |
add a comment |
$begingroup$
The 'non-midpoint' ground of the secondary transformer should have the same potential as the ground of the Arduino just like analogsystemsrf has done. Otherwise, who knows what kind of voltages you could see at the ADC of the Arduino?
Also, since this is AC, and the 'positive/top' side of the transformer would go negative with respect to the secondary ground, so you need a rectifier so the ADC pin does not go below ground. A series cap like analogsystemsrf would eliminate DC bias.
Edit: Another method (without rectifying) is to add a DC bias of 2.5V so that the signal goes above and below 2.5V (but not abober 5V or below 0V) you could then read both the positive and negative signal while maintaining a safe 0-5V for the ADC. Look up adding a DC bias on Google for many references, but it's basically a voltage divider with the midpoint connected to the signal you want to bias.
answered Mar 23 at 22:55
AdvancedNewbieAdvancedNewbie
33
$endgroup$
add a comment |
$begingroup$
The 'non-midpoint' ground of the secondary transformer should have the same potential as the ground of the Arduino just like analogsystemsrf has done. Otherwise, who knows what kind of voltages you could see at the ADC of the Arduino?
Also, since this is AC, and the 'positive/top' side of the transformer would go negative with respect to the secondary ground, so you need a rectifier so the ADC pin does not go below ground. A series cap like analogsystemsrf would eliminate DC bias.
Edit: Another method (without rectifying) is to add a DC bias of 2.5V so that the signal goes above and below 2.5V (but not abober 5V or below 0V) you could then read both the positive and negative signal while maintaining a safe 0-5V for the ADC. Look up adding a DC bias on Google for many references, but it's basically a voltage divider with the midpoint connected to the signal you want to bias.
answered Mar 23 at 22:55
AdvancedNewbieAdvancedNewbie
33
$endgroup$
add a comment |
$begingroup$
The 'non-midpoint' ground of the secondary transformer should have the same potential as the ground of the Arduino just like analogsystemsrf has done. Otherwise, who knows what kind of voltages you could see at the ADC of the Arduino?
Also, since this is AC, and the 'positive/top' side of the transformer would go negative with respect to the secondary ground, so you need a rectifier so the ADC pin does not go below ground. A series cap like analogsystemsrf would eliminate DC bias.
Edit: Another method (without rectifying) is to add a DC bias of 2.5V so that the signal goes above and below 2.5V (but not abober 5V or below 0V) you could then read both the positive and negative signal while maintaining a safe 0-5V for the ADC. Look up adding a DC bias on Google for many references, but it's basically a voltage divider with the midpoint connected to the signal you want to bias.
answered Mar 23 at 22:55
AdvancedNewbieAdvancedNewbie
33
$endgroup$
The 'non-midpoint' ground of the secondary transformer should have the same potential as the ground of the Arduino just like analogsystemsrf has done. Otherwise, who knows what kind of voltages you could see at the ADC of the Arduino?
Also, since this is AC, and the 'positive/top' side of the transformer would go negative with respect to the secondary ground, so you need a rectifier so the ADC pin does not go below ground. A series cap like analogsystemsrf would eliminate DC bias.
Edit: Another method (without rectifying) is to add a DC bias of 2.5V so that the signal goes above and below 2.5V (but not abober 5V or below 0V) you could then read both the positive and negative signal while maintaining a safe 0-5V for the ADC. Look up adding a DC bias on Google for many references, but it's basically a voltage divider with the midpoint connected to the signal you want to bias.
answered Mar 23 at 22:55
AdvancedNewbieAdvancedNewbie
33
edited Mar 23 at 23:47
answered Mar 23 at 22:55
AdvancedNewbieAdvancedNewbie
33
answered Mar 23 at 22:55
AdvancedNewbieAdvancedNewbie
33
answered Mar 23 at 22:55
AdvancedNewbieAdvancedNewbie
33
33
add a comment |
add a comment |
$begingroup$
if u r measuring Ac Voltage corresponding to AC Main i will suggest u please used diode bridge and filter capacitor at secondary side.
1. u will get DC voltage corresponding to AC mains
2. In your circuit opamp o/p getting loaded because of transformer secondary winding when your AC Mains not available. that's why your reference is changing.
answered Mar 24 at 2:58
Aditya Suresh RajpurkarAditya Suresh Rajpurkar
1
$endgroup$
add a comment |
$begingroup$
if u r measuring Ac Voltage corresponding to AC Main i will suggest u please used diode bridge and filter capacitor at secondary side.
1. u will get DC voltage corresponding to AC mains
2. In your circuit opamp o/p getting loaded because of transformer secondary winding when your AC Mains not available. that's why your reference is changing.
answered Mar 24 at 2:58
Aditya Suresh RajpurkarAditya Suresh Rajpurkar
1
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if u r measuring Ac Voltage corresponding to AC Main i will suggest u please used diode bridge and filter capacitor at secondary side.
1. u will get DC voltage corresponding to AC mains
2. In your circuit opamp o/p getting loaded because of transformer secondary winding when your AC Mains not available. that's why your reference is changing.
answered Mar 24 at 2:58
Aditya Suresh RajpurkarAditya Suresh Rajpurkar
1
$endgroup$
if u r measuring Ac Voltage corresponding to AC Main i will suggest u please used diode bridge and filter capacitor at secondary side.
1. u will get DC voltage corresponding to AC mains
2. In your circuit opamp o/p getting loaded because of transformer secondary winding when your AC Mains not available. that's why your reference is changing.
answered Mar 24 at 2:58
Aditya Suresh RajpurkarAditya Suresh Rajpurkar
1
answered Mar 24 at 2:58
Aditya Suresh RajpurkarAditya Suresh Rajpurkar
1
answered Mar 24 at 2:58
Aditya Suresh RajpurkarAditya Suresh Rajpurkar
1
answered Mar 24 at 2:58
Aditya Suresh RajpurkarAditya Suresh Rajpurkar
1
1
add a comment |
add a comment |
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Where did you get the circuit? I'd like to see the original. It will not work at all as drawn.
If all you want is 5v you just need your transformer connected to a bridge rectifier. The low output of the bridge rectifier will be your ground. Then you connect a 7805 regulator and a cap before and after and walla! You have a nice 5v 1A power supply.
(https://i.stack.imgur.com/eiwzE.png)
answered Mar 24 at 17:32
TpKnetTpKnet
1015
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1
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It's not a power supply. OP is presumably trying to isolate, step down, and bias the mains voltage to midscale for the analog-to-digital input.
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– Spehro Pefhany
Mar 24 at 17:42
add a comment |
$begingroup$
Where did you get the circuit? I'd like to see the original. It will not work at all as drawn.
If all you want is 5v you just need your transformer connected to a bridge rectifier. The low output of the bridge rectifier will be your ground. Then you connect a 7805 regulator and a cap before and after and walla! You have a nice 5v 1A power supply.
(https://i.stack.imgur.com/eiwzE.png)
answered Mar 24 at 17:32
TpKnetTpKnet
1015
$endgroup$
1
$begingroup$
It's not a power supply. OP is presumably trying to isolate, step down, and bias the mains voltage to midscale for the analog-to-digital input.
$endgroup$
– Spehro Pefhany
Mar 24 at 17:42
add a comment |
$begingroup$
Where did you get the circuit? I'd like to see the original. It will not work at all as drawn.
If all you want is 5v you just need your transformer connected to a bridge rectifier. The low output of the bridge rectifier will be your ground. Then you connect a 7805 regulator and a cap before and after and walla! You have a nice 5v 1A power supply.
(https://i.stack.imgur.com/eiwzE.png)
answered Mar 24 at 17:32
TpKnetTpKnet
1015
$endgroup$
Where did you get the circuit? I'd like to see the original. It will not work at all as drawn.
If all you want is 5v you just need your transformer connected to a bridge rectifier. The low output of the bridge rectifier will be your ground. Then you connect a 7805 regulator and a cap before and after and walla! You have a nice 5v 1A power supply.
(https://i.stack.imgur.com/eiwzE.png)
answered Mar 24 at 17:32
TpKnetTpKnet
1015
answered Mar 24 at 17:32
TpKnetTpKnet
1015
answered Mar 24 at 17:32
TpKnetTpKnet
1015
answered Mar 24 at 17:32
TpKnetTpKnet
1015
1015
1
$begingroup$
It's not a power supply. OP is presumably trying to isolate, step down, and bias the mains voltage to midscale for the analog-to-digital input.
$endgroup$
– Spehro Pefhany
Mar 24 at 17:42
add a comment |
1
$begingroup$
It's not a power supply. OP is presumably trying to isolate, step down, and bias the mains voltage to midscale for the analog-to-digital input.
$endgroup$
– Spehro Pefhany
Mar 24 at 17:42
1
1
$begingroup$
It's not a power supply. OP is presumably trying to isolate, step down, and bias the mains voltage to midscale for the analog-to-digital input.
$endgroup$
– Spehro Pefhany
Mar 24 at 17:42
$begingroup$
It's not a power supply. OP is presumably trying to isolate, step down, and bias the mains voltage to midscale for the analog-to-digital input.
$endgroup$
– Spehro Pefhany
Mar 24 at 17:42
add a comment |
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2
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Reads some mV relative to what? Arduino ground? If so, you either have a short to ground somewhere, you are accidentally driving the pin low, or you have killed the I/O pin.
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– jms
Mar 23 at 12:30
1
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Double-check your wiring. If you built this on a breadboard socket, it's possible you have a wire in a hole next to the one it actually belongs in. It happens more often than you might think.
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– Dave Tweed♦
Mar 23 at 12:43
2
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What's the winding ratio of your "AC-AC adapter" (which I'd prefer to call a "transformer").
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– Marcus Müller
Mar 23 at 12:46
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Please re-write you question using separate sentences to describe which conditions work and which conditions do not work. Does the circuit work correctly when the AC adapter is connected and powered up? Does the circuit work correctly when the AC adapter is connected but not powered? What is the input impedance of the Arduino analog input pin?
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– AnalogKid
Mar 23 at 14:15
1
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Disconnect the Arduino pin, leave everything else, and make a measurement at the voltage divider output. Divide and conquer.
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– Spehro Pefhany
Mar 23 at 19:51